Recently, with westernization of diets, patients of lifestyle-related disease are increasing, resulting in serious medical and social problems. At present, in Japan, the number of diabetic patients is 8,000,000, and the number of diabetic patients plus pre-diabetic patients is 20,000,000. The three main complications of diabetes are retinopathy, nephropathy, and neuropathy. Diabetes is also a cause for arteriosclerosis. Furthermore, diabetes may cause heart diseases and brain diseases.
A person develops diabetes in such a manner that improper diets and life styles, secretion from fat cells due to fatness, or oxidative stress decrease the function of pancreas, causing shortage of insulin that controls blood glucose level or reducing the effect of insulin. Diabetes has symptoms such as frequent urination and increased amount of urination, and increased thirst. However, such symptoms may not enable patients to realize that they develop diabetes, and most patients know their illness when they are subjected to inspection in hospitals etc. This tells why there are so many “silent” diabetic patients.
However, at the stage where abnormal symptoms resulting from the complications of diabetes are found in hospitals etc., conditions of the disease have advanced too far, making it difficult to completely cure the disease. In particular, many of the complications of diabetes are difficult to cure, and therefore prevention of diabetes is considered as important like many lifestyle-related diseases. For the prevention, early identification and early determination of therapeutic effect are essential, and there are many inspections for diabetes for this purpose.
When blood contains abnormal amounts of carbohydrates and lipids therein, oxidative stress causes (A) a protein and (B) a carbohydrate or a lipid to react with each other, so that a glycated protein is generated. The glycated protein is repeatedly dehydrated and condensed, so that AGEs (advanced glycation end products) are produced. AGEs are end products produced via nonenzymatic glycosylation reaction of protein (Maillard reaction). The glycated protein and a part of AGEs exhibit yellowish brown color, emit fluorescence, and form crosslink by binding to nearby proteins. Further, AGEs have such a biochemical property that AGEs are recognized by an AGEs receptor.
It can be said that AGEs are deposited on and invade a blood vessel wall, so as to affect macrophage partially responsible for an immune system. This causes, for example, an inflammation while releasing cytokine which is a protein, and ultimately causes arteriosclerosis to develop.
In particular, it is found that AGEs derived from aldehydes are particularly accumulated on a lesion area caused by a diabetic complication, so that such AGEs are advocated as an important component of the progress of a complication (see Non-Patent Literature 1). Such AGEs having biological toxicity is, in particular, called “TAGEs (toxic AGEs)”.
As such, there is suggested a possibility that a glycated protein, a glycated amino acid, and AGEs etc. are used as an indicator of a health condition. Studies regarding a health condition on the basis of kinds of AGEs, an abundance of AGEs in a human body, etc. have been intensively carried out. In the case of diabetes, as the blood glucose level increases, the amount of AGEs increases. Accordingly, by monitoring AGEs, it is possible to identify diabetes at an early stage or comprehend progress of diabetes. In recent years, there have been developed some methods for monitoring glycated protein, glycated amino acid, AGEs, etc. One example of a method for screening diabetes mellitus by monitoring AGEs is disclosed in Patent Literature 1.
In this method, AGEs are monitored in such a manner that skin of a forearm is irradiated with excitation light and a spectrum of fluorescence from AGEs binding to skin collagen is detected, and the spectrum of the fluorescence thus measured and a predetermined model are compared with each other. This makes it possible to obtain data of AGEs in a non-invasive manner.
Note that Patent Literatures 2 to 4 disclose a living body measurement device which visualizes a blood vessel and includes a plurality of LEDs (light emitting diodes) each having a different wavelength.